Browser setting to prevent movement

Hello all,

As part of a review of CSS Animations Level 1
<https://www.w3.org/TR/css-animations-1/> and CSS Transforms Module Level 1
<https://www.w3.org/TR/css-transforms-1/>, the APA Working Group identified
a potential gap that could be filled by the various specifications that
deal with movement of any kind.

WCAG 2.0 Success Criterion 2.2.2 Pause, Stop, Hide states that:

For moving, blinking, scrolling, or auto-updating information, all of the
> following are true:
>
>    - *Moving, blinking, scrolling*
>
>
>    - For any moving, blinking or scrolling information that (1) starts
>    automatically, (2) lasts more than five seconds, and (3) is presented in
>    parallel with other content, there is a mechanism for the user to pause,
>    stop, or hide it unless the movement, blinking, or scrolling is part of an
>    activity where it is essential;
>
>
>    - *Auto-updating*
>
>
>    - For any auto-updating information that (1) starts automatically and
>    (2) is presented in parallel with other content, there is a mechanism for
>    the user to pause, stop, or hide it or to control the frequency of the
>    update unless the auto-updating is part of an activity where it is
>    essential.
>
> The APA thinks that there would be a benefit to having a single in-browser
mechanism for pausing or preventing the playing of any and all animation,
including that authored with CSS, animated GIFs, and Video content.

We'd like to open this discussion to the wider CSS A11Y task force. A
number of questions come to mind. Is this idea reasonable? Is it likely to
be implemented by browser vendors? Could the prefers-reduced-motion media
feature <https://drafts.csswg.org/mediaqueries-5/#prefers-reduced-motion>
be used as the basis for such a feature? Could this work without requiring
action by the author? Is this something that should be included in the
various CSS modules that deal with movement or animation of some sort.

Thanks in advance for any thoughts or feedback.

Ian.